THE CONCRETE COVER CHANGING EFFECT ON THE SEISMIC PARAMETERS OF RC COLUMNS STRENGTHENING WITH FIBER REINFORCED POLYMER SHEETS AND BARS

Reinforced concrete structures are strengthened in differentways. Near surface method (NSM),FRP con-nements are some of these ways. Studies show thatthe use of FRP for the connement of columns increasesboth the load carrying capacity,ductility.Former studies in the eld of using FRP bars by applyingNSM method show that these bars increase thecolumns exural capacity. Despite increasing bendingcapacity by NSM-FRP bars, this method of strengtheningleads to decreasing ductility,energy dissipationcapacity of the columns. Besides the aforementionedshortcomings of this method, the lack of completeusage of load-carrying capacity of FRP bar is anotherdeciency of the aforementioned method in whichthis deciency is removed by compounding this methodwith CFRP connement. In the experimental part ofthe study, ve specimens of square reinforced concretecolumn strengthened by the methods of NSM-GFRPand NSM-GFRP in combination with CFRP connement,the eect of concrete covering on the load-bearingcapacity, initial stiness, ductility,energy dissipationcapacity were assessed. Also, hysteresis curves andLoad-versus-drift ratio envelope curves were comparedwith each other. The specimens, under cyclic uniaxialexure with constant axial load, were tested untilfailure. The results show that the use of both strengtheningmethods increases the columns carrying capacity.However, the NSM-GFRP method decreases energy dissipationcapacity,ductility of the columns. Contraryto this method, the CFRP connements in combinationwith the NSM-GFRP would increase the ductility andenergy dissipation capacity, indicating that this is oneof the useful methods for strengthening of the structure.Also, the results show that with the increase of the concretecover from 20 to 40 mm, load-bearing capacity,ductility,energy dissipation capacity would be reducedin both strengthening methods. With the increaseof concrete cover from 20 mm to 40 mm, carrying capacity,ductility,energy dissipation capacities of 10,3,18% for specimens strengthened by NSM-GFRPmethod,of 25, 40, 33 % for specimens strengthenedwith the combination method of NSM-GFRP,CFRPconnement would reduce, respectively. Thus, the eectof concrete cover on combinatory reinforcing method ishigher.